Type 1 diabetes (T1D) is particularly challenging to study directly in humans. By the time a patient is diagnosed with T1D, the destruction of beta cells by the immune system is nearly complete, rendering it difficult to investigate the mechanisms by which the disease develops. To address this, we propose to develop a novel humanized mouse model of T1D that permits study of the in vivo generation and function of human islet autoreactive T cells. This new model is based on recent technological breakthroughs. 1) Generation of human islet autoreactive T-cell clones. 2) Development of lentiviral technology enabling efficient transduction of human hematopoietic stem cells (HSC). 3) Availability of novel NOD-scid IL2rgnull (NSG) mice that support the generation of a functional human immune system following engraftment with human HSC. 4) Development of a human fetal liver/thymus/pancreas model in which a human immune system is generated in the presence of an autologous, functioning human pancreas. Combining these new cutting edge technologies, we will generate human TCR-transgenic (retrogenic) mice engrafted with a functional human immune system enriched in human TCR transgenic (Tg) autoreactive T cells. To accomplish this, we have developed next generation genetically modified NSG mice, including HLA Tg NSG mice. We have established lentiviral transduction of human HSC in our laboratory, and have cloned into the virus (a) TCRs from HLA-A2-restricted CD8 T cell clones specific for human IGRP265-273; (b) TCRs from HLA-DR4-restricted CD4 T cell clones specific for human GAD555-567 and (c) a positive control HIV-specific TCR. We have also developed a spontaneously diabetic NRG-Akita mouse strain that can be engrafted with human fetal liver, thymus, and pancreas to generate a human immune system that develops in the presence of the autologous human fetal pancreas graft that matures and regulates glucose homeostasis. We will use these new technologies to generate retrogenic NSG-HLA Tg mice engrafted with a human immune system expressing Tg TCRs against IGRP265-273 or GAD555-567. We will test the overall hypothesis that human TCR Tg autoreactive CD4 and CD8 T cells either alone or together will induce diabetes in humanized mice. Specific Aim 1 will assemble and validate the components needed to create retrogenic mice with human T1D reactive immune systems. Specific Aim 2 will determine whether the human TCR retrogenic models develop insulitis or T1D and will analyze the ability of environmental perturbations to modulate this process. These studies will lead to the development of a humanized mouse model of T1D in which all of the human immune components are present to participate in disease initiation and progression. The results of this study will provide an important pre-clinical model system for investigation of T1D development without putting patients at risk. The generation, validation, and use of these new animal models will permit investigation of mechanisms that regulate human autoreactive T cell development and function and provide insights into how therapeutics may modulate this process.